Cathode ray television apparatus with adjustable size of the image point



Dec. 31, 1940. K. SCHLESINGER 2,227,005 CATHODE RAY TELEVISION APPARATUS WITH ADJUSTABLE SIZE OF THE IMAGE POINT Filed May 19, 1936 2 Sheets-Sheet 1 Jared/0r.

CATHODE RAY TELEVISION APPARATUS WITH ADJUSTABLE SIZE OF THE IMAGE POINT Filed May 19, 1936 2 Sheets-Sheet 2 1940. K. SCHLESINGER 2,227,005

HELA X4 770 OSCILLA T lO/V GHQ/ERA TO}? Jared/06' Patented Dec. 31, 1940 PATENT orrlca CATHODE RAY TELEVISION APPARATUS WITH ADJUSTABLE SIZE OF THE IMAGE POINT Kurt Schlesinger, Berlin, Germany, assignor, by mesne assignments; to Loewe Radio, Inc., a corporation of New York Application May 19, 1936, Serial No. 80,582 In Germany May 22, 1935 4 Claims.

This invention relates to television apparatus comprising a cathode-ray tube as picture scanning and/or shading means and has for its object to adapt such apparatus for the reception of television pictures of dilferent definition. The invention therefore provides for changes in the size of the picture element so that. if a changeover is desired to be made from a large number of scanning lines to a small one, the size of the image spoL nay be increased in order to maintain a uniform line screen without empty spacesbetween the lines, and so that, on the other hand,

' if a change-over is desired to be made from a small number of scanning lines to a large one, the

size of the image spot may be reduced in order to prevent the scanning lines from overlapping. The invention further provides means for keeping the maximum light intensity of the picture constant in spite of the variations set forth in the 2.0 size of the image spot.

As is well known, the size of the image formed by a lens of a given object, taken in one linear coordinate, is, in common glass lenses, equal to the size of this object, taken in the same coordi- 35 nate, multiplied by the quotient of the distances between lens and image on the one hand, lens and object on the other hand. This law is 'applicable to electron optical reproduction in a modified form. The modification consists in the introduction of the electron speed quotient, i. e. the quotient of the electron speeds at the object-and at the picture receiving plane. In the figure representing the size of the image, the size of the object has to be multiplied by this speed quotient. In other words, if the ratio between the electron speed at the object of electron optical reproduction and the electron speed at the picture receiving plane is reduced, other data being 7 kept constant, the size of the image spot is reduced. The electron speed in the picture receiving plane is, in conventional cathode ray tubes, substantially equal to the square root of the final accelerating anode potential relatively to the cathode of the tube. The object of electron optical reproduction is, in cathode ray tube apparatus embodying the present invention, the aperture in a diaphragm. The electron speed at this object is substantially equal to the square root of the potential of the diaphragmrelatively to the oathode.

With these facts inmind, the invention provides'for variability of the potential of the diaphragm, the aperture of which forms the object as of "which the image spot is an electron image, so

that the speed of the electrons at this diaphragm, and thus the scale of electrons optical reproduction, can be adapted to any desired number of scanning lines as indicated above.

In the following more detailed explanation and 6 description of the invention, reference will be had to the accompanying drawings, whereof Fig. 1 is a schematic view of a cathode ray tube as far as its parts are of interest for the present purpose, and of some essential circuit elements, 10 whereas Fig. 2 shows the operating circuits designed according to the invention in more detail.

Fig. 1 shows an intermediate diaphragm l, the aperture of which is reproduced on the luminous 15 screen 5 by means of an electrostatic lens comprising a tubular member 2 with an apertured plate 3 inserted thereinto and an anode 4 located in front of the same. The aperture in the diaphragm I is caused to act as an electron emitting surface by concentrating onto said aperture a beam of electrons with the assistance of a device corresponding to the condenser optic of a projection apparatus. For this purpose there may conveniently be employed a preliminary anode l and 25 a cylinder 8, the bias of the diaphragm I being always maintained more positive than the bias of the cylinder 8, which may be connected with the cathode 6. By providing the preliminary anode l, constancy of the current intensity independso I ently of variations in the bias I of the dia--. phragm, is ensured. If the cathode 6 is assumed to be earthed, a variable (adjustable) bias may be applied to the diaphragm I by means of the battery I. According to the invention, this bias 35 l' is made to be variable (adjustable). The bias of the tubular member 2-3 is derived from the anode potential of the anode battery 4. For this purpose there is employed in accordance with the invention a potentiometer the tapping point 9 of 40 which is adjusted once-for all. By thus once adjusting the distribution of the potential l (9) it may be accomplished that the image of the diaphragm l is always produced sharply on the luminous screen 5 even if the bias of the diaphragm 45 l is varied. The potentiometerhaving the tapping 9 may also be fitted within the tube.

The above explanations regarding the scale of electron-optical reproduction are applied to the structure shown, as follows? 50 The size of the image point appearing on 5 is not governed alone by the distance from the object l to the lens 4 and the distance from the lens 4 to the image 5, but in working out the ratio between thelinear dimensions of ima e and object, the linear dimensions of the object have still to be multiplied by the factor i. e. the square root of the quotient of the potentials (relatively to cathode 6) of the diaphragm I and the anode 4. It is accordingly possible with a given size of the diaphragm aperture I and likewise given spacings 4 to 5 and 1 to 4 to vary the size of the point on the screen by varying the bias I of the diaphragm I from the exterior.

Whilst the above mentioned importance of the factor for the electron optical conditions has already been referred to in the literature, it has not become known that with a reduction of the bias I the light intensity of the image point greatly decreases. The increase in the light density of the image point caused by the reduction in size of the image point is not capable of counter-balancing the decrease in the total energy caused by the reduction of the potential at I. According to a further feature of the invention, therefore, a coupling is performed between the anode potential 4 and the bias I' with the result that the light current proceeding from the image point always remains constant. In this connection it is to be remembered that with an increase of the anode potential 4' the sensitivity of deflection of the tube is decreased. If, therefore, it is to be avoided that the picture becomes smaller, the relaxation oscillations which cause the deflection require to be increased. The picture size remains constant if the relaxation oscillation amplitude is increased in proportion to the anode potential 4'.

A mains supplied circuit according to the invention which fulfills all of these requirements is illustrated in'Fig. 2. There is employed for the generation of the image field a potential-doubling circuit the dimensioning of which, more particularly for television purposes, has already been previously described (see co-pending patent applications numbered 39,467/35, filed September 6, 1935; and 53,535/35, filed December 9, 1935). A transformer l0 causes the charging of two condensers l3 and I4 through the medium of two rectifier valves II and I2. The primary winding l5 of this transformer is connected to the terminals l8 and IQ of the alternating current mains over a selector switch 20 the function of which will be explained below. During one half period of the alternating voltages excited at the secondary winding of the transformer III the rectifier II is conductive and charges the upper armature of the condenser I3 positive relatively to its lower armature. During the other half period the rectifier I2 is conductive and charges the lower armature of the condenser ll negative relatively to its upper armature. The useful anode voltage 4', which is to be applied to the anode 4 of the television tube, is accordingly the sum of the voltages built up across i3 and I4, and these condensers need each be tested in respect of only one half of the required anode voltage, which reduces the cost of these condensers considerably. According to a subsidiary feature of the preset invention, the heating of the rectifiers II and I2 is performed not by the transformer l0, but by a separate transformer or by special batteries in constant strength. For the sake of simplicity heating batteries are not shown in the drawings. The primary coil I! of the transformer is provided with a plurality of tappings lia, lib, etc. each connected to a terminal of the switch 20. According as the switch 5 20 connects the conductor 2| to the terminal a. b, or c, the exciting voltage is applied between the right hand end of the winding l5 and the tapping point lia, lib, or lie. The maximum value of the voltage excited at the secondary 10-- winding of i0 is obviously obtained in the position a. In this position the switch 20 at the same time connects the conductor 22 (which is connected to the diaphragm I of the television tube) to the tapping point Ila of the potentiometer II. The fraction I, applied to the diaphragm I, of the total anode voltage 4', applied to the anode 4, is accordingly at a minimum when the switch is in the position a. It will thus be seen that by means of the switch 20 and with a suitable selection of the tapping points lie to c and l'la to c the desired result can be obtained if so adjusting the potentials of l and l in opposite senses that changes in the potential of i do not aifect the luminosity of the reconstructed television picture. The voltage of the electrostatic lens is, in accordance with the invention, so adjusted once and for all by tap 9 that the image point appears sharply on the screen. One half of the anode potential is taken from the condenser ll 30 and is conducted to a relaxation oscillation generator which is designated ll. This generator supplies to the Braun tube, at the terminals 11 and x, deflecting voltages, the amplitudes of which are proportional to the direct potential supplied to I and accordingly remain in a permanently constant ratio to the anode potential, so that any variations of the anode potential leave the size of the scanning line screen unaltered. There is accordingly obtained the desired 40 result which consists in the following:

Increase of the definition by reduction of the image point with the aid of electron-optical means, with the size and brightness of the picture remaining constant, corresponding with an increase in the number of image lines to be transmitted with constant picture size. The picture size is always so adjusted-that the lines just touch each other. In the case of the smallest number of lines the diaphragm l is directly connected with the anode 4 (position 0 ofswitch 20). The anode potential 4' is then the smallest occurring, because the maximum number of primary turns of transformer II are then in the circuit. This minimum anode potential is so adjusted that the maximum brightness the image is satisfactory.

I claim:

1. A television receiver including a cathode ray picture tube wherein a predetermined and substantially fixed picture area is scanned and wherein it may be desirable to vary, over a considerable range, the number of lines scanned on the picture area comprising means inthe cathode ray tube adapted to generate a focused beam of electrons, said means including a cathode, an anode diaphragm, a first accelerating anode and a second accelerating anode, means for deflecting the cathode ray beam, means for-generatin deflecting voltages for energizing the beam deflecting means, a source of potential, means including said source of potential for maintaining said second accelerating anode and said anode diaphragm positive with respect to said cathode by diiierent predetermined selectable amounts, (6

creasing as the potential of thesecond acce1erating anode is increased, means for maintaining said first accelerating anode at a positive potential with respect to said cathode by a fixed fractional amount of the potential of said second accelerating anode, whereby the diameter of the cathode ray beam at the potential point will vary as an inverse function of the potential of the said second accelerating anode, and means for varying the amplitude of the cathode ray beam deflecting voltage as a function of the potential of the second accelerating anode.

2. A system for use with a cathode ray tube wherein the cross sectional area of the cathode ray beam at the focal point may be varied comprising means in the cathode ray tube adapted to generate a focused beam of electrons, said means including a cathode, an anode diphragm, a first accelerating anode and a second accelerating anode, a source of potential, means including said source of potential for maintaining said second accelerating anode and said anode diaphragm positive with respect to said cathode by different predetermined selectable am ts,the difierential potential between the second accelerating anode and said anode diaphragm decreasing as the potential of the second accelerating anode is decreased, and means for maintaining said first accelerating anode at a positive potential with respect to said cathode by a fixed fractional amount of the potential of said second accelerating anode, whereby the diameter of the cathode ray beam at thefocal pointmaybevarledininverse proportion to the potential of the said second accelerating anode.

3. A television system including a cathode ray tube. means in said tube adapted to generate a focused cathode ray beam comprising a cathode, an anode diaphragm. a first accelerating anode and a second accelerating anode, a source of poanode diaphragm to predetermined fixed points along said potentiometer in accordance with the selected potential applied to said second accelerating anode so that the differential potential betweenthe second accelerating anode and the anode diaphragm increases with increase in the potential applied to said second anode, and means for connecting said cathode to the point of fixed potential, whereby the cross-sectional area. of the focused cathode ray beam at the focal point is an inverse function of the intensity of the potential applied to said second accelerating anode.

4. A television system including a cathode ray tube, means in said tube adapted to generate a focused cathode ray beam comprising a cathode, beam deflecting means for causing deflection of the generated cathode ray beam in substantially mutually perpendicular directions, an anode diaphragm, a first accelerating anode and a second accelerating anode, a source of potential having positive and negative terminals, means for selectively changing the efiective intensity of the potential source in predetermined steps, means for connecting the positive terminal of the source of potential to the second accelerating anode, means for connecting the negative terminal to a point of fixed potential, means for applying a positive potential to said first accelerating anode, the applied potential bearing a fixed relation to the potential applied to said second accelerating anode, a potentiometer connected across said source of potential, means for connecting said anode diaphragm to predetermined fixed points along said potentiometer in accordance with the selected potential applied to said second accelerating anode so that the potential diflerence between the second accelerating anode and the anode diaphragm is decreased when the potential applied to said second anode is decreased, means for connecting said cathode to the point of fixed potential, whereby the cross-sectional area of the focused cathode ray beam at the focal point is an inverse function of the intensity of the potential applied to said second accelerating anode, means for generating deflection voltage variations for energizing the beam deflecting means. and means for applying different operating potentials to said last named means in accordance with the selected potential applied to said second accelerating anode. KURT SCHLESINGER. 

